1. Field of the Invention
The present invention relates to a positioning mechanism between an eye to be inspected and a measurement system or an inspection system of an ophthalmologic apparatus, and particularly relates to a mechanism for controlling an up/down (hereinafter referred to as "vertical") movement in such an ophthalmologic apparatus.
2. Description of the Related Art
In an ophthalmologic apparatus such as a fundus camera or the like, there is provided a mechanism for performing positioning of a measurement system or an inspection system relative to an eye to be inspected. The range of vertical movement required in an ophthalmologic apparatus is generally about 30 mm, and to this end, conventionally, a mechanical mechanism using a feed screw is known. That is, in such a mechanical mechanism, a rotary portion is provided on the outer periphery of an operation rod called a joy stick and the rotating movement of the rotary portion is transmitted to a vertical movement mechanism through a combination of belts and/or gears. In such a system, the relationship between the rotated angle of a vertical movement knob and the quantity of vertical feeding is fixed.
Further, in some of so-called refractometers and keratometers, there has been a proposal of a device in which a vertical movement mechanism is motor-driven. In this device, the speed can be switched between two, high and low, stages. A rotary knob is provided on the upper side of a joy stick so that a low speed vertical movement is carried out at a predetermined rotated angle of the rotary knob, while a high speed vertical movement is carried out at another predetermined rotated angle of the rotary knob.
Further, there is another example of device in which an exclusive use vertical movement knob is provided on the lower side of a joy stick so that the relationship between the quantity of rotation of the knob and the rotation number of a vertical movement motor is set so as to be linear.
The above-mentioned mechanical vertical movement mechanism has a problem in that it is complicated in structure, while it is advantageous in that the operation property is good because the relationship between the inspector's operation and the quantity of movement is linear and the speed of movement can be adjusted freely.
The above-mentioned device in which the relationship between the quantity of rotation of the knob and the rotation number of a vertical movement motor is set so as to be linear has another problem because it takes a long time for the movement to a necessary position, while the device is advantageous in that it is simple in structure. That is, in such a device as a non-contact tonometer in which strict positioning is required, it is necessary that the rotary knob is rotated many times so as to carry out vertical movement comparatively largely in the case where many subjects different in hight from one another are to be inspected successively.
Further, in the device in which the speed of vertical movement can be switched between two, low and high, speed stages, the operation is troublesome because the switching between low and high speed stages must be decided in accordance with the judgement by the inspector per se, and this device is inferior to the mechanical vertical movement mechanism in view of operation property because the content of operation and the quantity of movement are difficult to coincide with the inspector's operation sense.
Related art can be listed as follows.
Japanese Patent Examined Publication No. 3-1689; Japanese Patent Examined Publication No. 2-88028; Japanese Patent examined Publication No. 2-88029; Japanese Patent Unexamined Publication No. 61-198322; U.S. Pat. No. 4,489,303; U.S. Pat. No. 4,748,323; U.S. Pat. No. 4,794,388; U.S. Pat. No. 4,584,510; U.S. Pat. No. 4,382,166; U.S. Pat. No. 4,533,827; U.S. Pat. No. 5,113,179; U.S. Pat. No. 4,616,115; U.S. Pat. No. 4,879,556; U.S. Pat. No. 5,008,534; U.S. patent application Ser. No. 07/910060 by Masahiro Sugimura, "Joy Stick Mechanism"; and U.S. patent application Ser. No. 08/052,916 by Yoshiaki Mimura, et al "Joy Stick Mechanism for Ophthalmic Apparatus", the disclosures of the above U.S. Patent Applications are incorporated herein by reference.